Molecular sieves are classified by the Structure Commission of the International Zeolite Association according to the rules of the IUPAC Commission on Zeolite Nomenclature. According to this classification, framework-type zeolites and other crystalline microporous molecular sieves, for which a structure has been established, are assigned a three letter code and are described in the Atlas of Zeolite Framework Types, 5th edition, Elsevier, London, England (2001).
Among said zeolitic materials, Chabazite is a well studied example, wherein it is the classical representative of the class of zeolitic materials having a CHA framework structure. Besides aluminosilicates such as Chabazite, the class of zeolitic materials having a CHA framework structure comprises a large number of compounds further comprising phosphorous in the framework structure are known which are accordingly referred to as silicoaluminophosphates (SAPO). In addition to said compounds, further molecular sieves of the CHA structure type are known which contain aluminum and phosphorous in their framework, yet contain little or no silica, and are accordingly referred to as aluminophosphates (APO). Zeolitic materials belonging to the class of molecular sieves having the CHA-type framework structure are employed in a variety of applications, and in particular serve as heterogeneous catalysts in a wide range of reactions such as in methanol to olefin catalysis and selective catalytic reduction of nitrogen oxides NOx to name some two of the most important applications. Zeolitic materials of the CHA framework type are characterized by three-dimensional 8-membered-ring (8MR) pore/channel systems containing double-six-rings (D6R) and cages.
U.S. Pat. No. 7,067,108 B2 discloses zeolites of Chabazite framework type. These zeolites are prepared by employing a specific seeding material, namely a crystalline material having a framework type other than Chabazite framework type, such as AEI type, LEV type, or OFF type.
U.S. Pat. No. 6,974,889 B1 on the other hand discloses a process for the manufacture of a crystalline molecular sieve, such as zeolites of structure type CHA or LEV, containing phosphorus in its framework, wherein a colloidal crystalline molecular sieve is used as seed material. In particular, said document teaches the use of seed crystals having the structure type LEV, OFF, or CHA, wherein said seed crystals should be as small as possible for controlling the particle size of the product as well as for accelerating its formation. Specifically, the synthesis of SAPO-34 is disclosed in said document using colloidal solutions of Chabazite crystals, of which the XRD would indicate a uniform particle size of 100×400 nm, and wherein the product is crystallized for a period of 60 hours.
Although considerable efforts have been made with respect to the synthetic methodologies for obtaining zeolitic materials having the CHA framework structure, there remains the need for finding novel preparation methods which are yet more efficient in providing high quality materials at a lower cost. This is a particularly challenging objective, in particular in view of the widespread use of said materials in mass-applications such as in the treatment of automotive exhaust gas and the like. Furthermore, the need is also given for the preparation of novel zeolitic materials having the CHA framework structure displaying new characteristics for use in known and future applications, in particular in the increasingly important field of catalysis.